Electrical apparatus for changing the length of and displacement of the optical axis in cinematography



June 6,1939.

w. F. ALDER 2,161,120 ELECTRICAL APPARATUS FOR CHANGING THE LENGTH 0FAND DISPLACEIENT 0F THE OPTICAL AXIS IN CINEMATOGRAPHY Filed Dec. vsheets-sheet 1 June 6, 1939. w. F. ALDER TUS FOR CHANGING THE LENGTH OFAND DISPLACEIENT ELECTRICAL APPARA or THE OPTICAL Axls- 1NGINEMATOGRAPHY Filed Dec. l5, 1954 '7 Sheets-Sheet 2 l l 'm I /H-Vefzfor1L U W E14/del' u l v l @www June 6, 1939. w F A'LDER 2,161,120

ELECTRICAL APPARATUS FOR CHANGNG THE LENGTH OF AND DISPLACEMENT OF THEOPTICAL AXIS IN CINEMATOGRAPHY -Filed Dec. 1s, 1954 v 7 sheets-sheet sfr 4 if y ./22 Ven/0r WFA/def' -June 6, 1939. w: F. ALDER 2,161,120ELECTRICAL APPARATUS FOR CHANGING THE LENGTHv OF AND` DISPLAGEMENT 0FTHE OPTICAL yAXIIS- 1N GINEMATOGRAPHY Filed D ec: 13 1934 '7Sheets-Sheet 4 agi fzzrezz/or .zu n M ,y WFA/def b-wwm" Aff/Offlaga.

June 6, 1939. w, F ALDER A TH 0F AND DISPLACEMENT ELECTRICAL APPARATUSFOR CHANGING THE LENG 0F THE OPTICAL AXIS IN CINEMATOGRAPHY Filed Dec.13, 1934 7 Sheets-Sheet 5 25J A Afforlzey.

June *6, L1939.

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Patented June 6, 1939 l ELECTRICAL APPARATUS FOR CHANGING THE LENGTH FAND DISPLACELIEN'Iv 0F THE OPTICAL AXIS RAPHY IN CINEMATOG- wiumn F.Alder, Alhama, cmi.

Application December 13, 1934, Serial No. 757,312

11 claims. (C1. en -16.6)

My invention relates to an improvement in motion picture photography bywhich I obtain an y alternate lengthening and shortening, and thuschanging the optical axis between the scene or objects to bephotographed and the camera lens,

and thus varying the effective length of the optical axis of the camera.I also obtain simultaneously therewith, a lateral and angulardisplacement of the optical axis between the scene or objects, the lensand the nlm on which the photograph is made.

An object of this procedure is to thus vary the length of the focal axisin regard to various real or imaginary planes in the scene or objects tobe photographed at right angles to the optical axis, and at the sametime, on account of varying the lateral and angular displacement of thisoptical axis, lateral displacements of the images are obtained onsuccessive panels or frames of the moving picture film, whereby, whenthe picture on 'the film is projected by a standard projector, theillusion of depth by separation of the pictures constituent planes isapparent.

A further object and feature of my invention is obtaining this change oflength, lateral and angular displacement of the optical axis by arelative reciprocation of a mirror or reflector and the camera lens, andthe scene or objects to be photographed. The relative reciprocation maycomprehend the reciprocation of one mirror or of a relativereciprocation of two mirrors, and such a reciprocation is preferablyrectilinear. For the sake of convenience I preferably use a standardmotion picture camera and reflect the light from the scene or objects tobe photographed from a fixed mirror onto a rectilinearly reciprocatingmirror, and from this latter mirror, through the optical system of thecamera.

In carrying out my invention I make use of certain natural phenomena ofthe human eye and perception, such as the persistence of vision and theresolving power of the human eye. By persistence of vision I mean theretention of an image in the human perception. This has already beenrelied'upon in motion picture photography to give the illusion ofmotion. However, so far as I am aware, no attempt has been made to usethe function of the resolving power ofthe human eye for the separationof planes constituting a motion picture on a theatre screen.

It has been found that substantially no human eye can separate twoobjects which lie within an angle subtended by "I0 seconds of arc.Therefore. if two objects are less than 'l0 seconds of arcapart relativeto the observer, the two objects or outlines cannot be distinguished onefrom another. If, in a picture projected on a screen, tv. o projectedimages, that is, their outlines, lie within 70 seconds of arc relativeto the eye of the observer, such observer cannot detect the lateraldisplacement of 'these images. However, when by my procedure, images onsuccessive frames or panels of a mot-ion picture are laterally displacedby such an amount that the images projected on a screen subtend an arcof less than '70 seconds from the eye of the observer, due to thepersistence of vision, the observer does not detect this lateraldisplacement of the image of one panel in reference to that of asucceeding panel, but the observer has the unconscious perception ofseeing not only the frontal points, but the marginal outlines of objectsor scenes protographed, and thus the observer gains the impression ofbi-lateral vision. l Thus, when objects of which a motion picture istobe obtained are located in different planes at righty angles to thecentral axis, through, for instance, the center of a panel in the filmand the lens, and my procedure is used by which the length of theoptical axis is lengthened and shortened and displaced laterally andangularly, the images formed on successive panels or frames of the nlmbecome displaced laterally re1- ative to the similar images on adjacentpanels and to each other. Therefore, in practice, when the displacementon successive panels is within 70 seconds of arc in regard to the cameralens. the projected motion pictures give the appearance or illusion ofnatural bi-lateral vision. This is due to combining the functions ofpersistence .of vision and resolving power of the eye.

In practice, I find I may increase the displacement of the same image onsuccessive panels of the moving picture nlm by considerably more than 70seconds of arc considering the camera lens as the center, this being dueto the fact that the pictures are viewed by projection on the screen atthe projection distance between the projector and the screen, and theviewing distance of the spectator from the screen materially redus thearc of the shifting image as viewed by the spectator, from that whichmay be employed on the lm without the observer being conscious of anylateral movement or vibration of the image.

In my invention I make use of certain optical laws; for instance, thatin photography by means of a mirror, the image formed by the mirror, ineiect, takes the place of the real object or scene. Optical axioms asrelates to plane mirrors are: (l) that the conjugate focal distances ofa plane mirror are equal; and, (2) if such a' mirror be displaced agiven distance Vparallel to itself, the two images will be displacedtwice the distance of displacement of the mirror. 'Iherefore, in effect,when making a motion picture and using a reciprocating mirror, thechange -of the focal length from the image to the lens and hence to theillm is exaggerated, and hence, although the object or scene to bephotographed may be at substantially a constant distance from the lens,

eyes, when viewing a projected picture taken by there is, in reality, inthe photograph produced, a

shifting in the distance of the virtual images formed by thereciprocating mirror. This, also, as above mentioned, causes a lateraland angular displacement of the real 'images on the photo;- graphicfilm.

This changing of the size of the images on the illm together'with thelateral and angular dis- .placement of the objects in different planestransversev to the optical axis, causes the human my procedure, toifunction 4somewhat the same as in normal bi-later'al vision whenviewing actual objects and scenes. 'I'he human eyes are never at restexcept for short periods of iltfull iixity. The axial length of focus isconstantly changing by an unconscious muscular accommodation so that thevision shifts constantly from near to the more remote planes of thescenes ofJ objects being viewed. Moreover, the observers attention srarelyfocused on a given point of,

Y screen produces the effect of there being a multiplicity of differentplanes, in the picture transverse to the optical axis and thus gives theillusion of natural bi-lateral vision. this unconscious muscular changein the focus 'of the human eyes tends to relieve the eye strain whichmost observers note when viewing the ordinary motion picture.

In the results obtained by my procedure, I make use of the penumbraformed on the screen of any 'definite image. It is to be remembered thatthe pictures on the screen are in realityA `formed by the shadow of theopaque, or more or less opaque, silver'depositV on the ilm. 'Ihesharpness of any photographic image is 'given by the size of thegranular interstices separating these opaque silver deposits which formtheY image, and even with the'flnest projection lenses and nest grainpositive emulsion there is a penumbra formed on a screen at ordinaryprojection and observation distances of about 1" width at 100 feetseparation between the projector and the screen. Ihis penumbra is causedin part by the sagittate edge of the image due to the granularstructurerof the film and the diffraction of light. Y

This penumbra effect prevents the formation of really sharp imageoutlines on the screen, which, however, ordinarily are not visible dueto the resolving power of the eyes of the observer at the ordinaryobservation distance, as the pe- -numbra rarely exceeds an angle of "I'seconds of arc from the observer. 'Ihis penumbra eiect aids ymyprocedure by permitting in eifect, a greater oscillation or vibration ofthe images on the screen without such oscillation, shifting orvibrationbeing observable by the spectators.

In carrying out my invention I believe I have made certain inventions inthe appliances for reciprocating a mirror and in its set-up and controlby a motion'picture camera. I prefer to ops crate my invention by arectilinear reciprocation of a single mirror which may receive lightdirncidentauy,

rectly from the scenes or objects to be photographed', but preferably bya xedileld mirror which reflects light from the scenes or objects ontothe movable mirror and from this latter mirror through the opticalsystem of the camera. The reciprocating mirror is preferably at restwhile each panel of the picture is being PhOiSO- graphed, and moves toanother positionl when the shutter of the camera is closed. Thus, themovable mirror occupies a diierent position in its reciprocating'movement for each panel or ,frame of the picture.

done by simultaneously reciprocating a counterweight structure insynchronism with the moving and stationary periods of the secondaryreecting mirror. v

I also in eiect, control the speed of reciprocation of the secondarymirror and its counterweight by a cushion construction, this beingpreferably an air cushion in which the reciprocation of themirror andthe counterweight when they are moving together, expel air under controlof a valve from an airchamber and on their movement apart,` suck airinto such air chamber. To

' do this the mirror and the counter weight reciprocate in alignedcylinders and have supporting stems in such cylinders.

My invention also comprehends a type of reciprocating electric motor inwhich there'are two synchronously acting electric coil assembliesinwhich a primary coil is used to develop a constant high magnetic fieldandE a secondary or amature coil changes in polarity-.and thus, inconjunction with the -magnetic field Ain an air gap.- causes thereciprocation of the mirror stem and hence the mirror, ,and thecounterweight stem and hence the counterweight. l

Another feature of my invention involves the control of the secondary orarmature ,coils by a commutator or the equivalent, actuated by orinsynchronism with the shutter and hence' the lm feed of a standardmotion picture camera. This commutator may preferably be driven by aro-l tatingshaft through a reduction gear train operated by the motionpicture camera which is usually driven by an electric motor. Thecommutator changes" the polarity of the movable armature coils connectedto each stem in oruer to move the mirror and its complementarycounterweight in one direction or the other, 4that is, to thrust themirror outwardly in relation tothe reciprocating electric motor or toretract the mirror inwardly.

My invention also includes an arrangement of the commutator withsuitable resistance in the secondary or movable amature coil circuits bywhich a suitable reductionof the energizing current of the movablesecondary or armature coils will only move the mirror a definite part ofits complete stroke, thus giving the intermediate stoppages or periodsof rest to the mirror between f theequivalent, and employ in the.energizing circuit for the moving amature or secondary coils an ammetergraduated to indicate the foreground distance, that is, the distancebetween the camera -lens and the objects or scenes to be photographed.

The instrument is calibrated so that when the energizing currentindicates a-value in accordance with any particular foregone distance,the

` also of the lateral and angular'displacement of various points of theimage formed on the illm.

movable secondary mirror will have a displacement between each period ofrest to give the correct change of the length of the focal axis andorder to visually readthe exact length Vof the stroke of the secondarymirror I employ a.A

visible scale graduated preferably in thousandths of an inch ormillimeters and adjacent this'scale I reciprocate a marker or indicatingdevice, this being preferably a marking line or the equivalent in anextension of the counterweight stem. Then, due to the function ofpersistence of vision, together with the vrapidity of reciprocation ofthe mirror and its counterweight and counterweight stem, the markershows a hazed or elongated marking, deilning the lengthof reciprocationbetween the two points of the scale. If the mirror reciprocates betweenthese two extremes of stroke at which extremes it is brought to rest,this indicating scale may be graduated to indicate directly the lengthof stroke, but if the stroke is divided into one or more periods ofrest, the scale would be graduated accordingly and thus the length ofmaximum stroke indicate the displacement distance between any twopositions of rest of the reciprocating mirror.

'Ihe visible scale is also graduated as to foreground distance and thusby noting the length of the mirror stroke relative to the foregrounddistance scale, a determination can-be made as to the correctdisplacement of the mirror between each period of rest to obtain thedesired change inthe focal axis and also in its lateral and anguiardisplacement.

A preferred manner of deiiningthe end of a stroke is by using astroboscope.

In a simplified construction I may use two field coils, each reacting ona movable armature coil Y secured to a single reciprocating stem, thesingle carrying the motor and mirror housing, the camera andtheelectrical assemblag. y My invention is illustrated in connection wi theaccolllimllyllgdrawings, in which: Y'

Fig. 1 is a horizontal section showing one form of my invention with acounter-balanced electric motor.

VFig. 2 is a wiring diagram for the motorof Fig. 1.

Fig. 3 is an alternative wiring diagram for a two-stroke motor.

Fig. 4 is an optical diagram.

Fig. 5 is a plan showing an' assembly of my invention with a camera.

Fig. 6 is a horizontal section which may be considered taken on the line6 6 of Fig. 'I in the direction of the arrows showing a singlereciprocating motor. Y

Fig. 7 is an elevation taken in the direction of the arrow 1 of Fig. 5,the camera and part vof the assembly being omitted.V

Fig. 8 is a vertical transverse section on the line l--l of Fig. 6 inthe direction of the arrows, the rheostat and ammeter being shown inelevation.

Fig. 9 is a vertical section on the line 9 9 of Fig. 5 in 'the directionof the arrows through the commutator assembly.

Fig, l0 is'a vertical section on the line III-II of Fig. 9 in thedirection of the arrows.

I Fig. l1 is a vertical section on the line II-II of Fig. 9 in thedirectionof the arrows.

Fig. 12 is a wiring diagram for the motor -of omitted, and it will beunderstood that any suitiialzile type of motion picture camera may beutied. Suitably supported or mounted in front of the optical system ofl,the camera I employ a mirror housing designated by the assemblynumeral 'Il 'I'his has a window frame I8 forming anY open end which hasa window glass I1. Light shades Il, if desired, may be attached to thewindow frame so that only the light from the scenes orv objects to bephotographed will enter the mirror housing. One side of the housing I9is preferably at and located in the housing and parallel thereto thereis a mirror holder 2l for the eld or primary mirror 2I. This mirrorshould be of a relatively large size in order to accommodate the largeareas required to be photographed in some cases. The housing has a rearwall 22 with a window opening 23 therein in which there is a smallwindow 2l through which the light is reflected through the opticalsystem of the camera. 'Ihis renection is from the moving or secondarymirror 25 which is held in a suitable mirror holder 2i. This holder ispreferably of light weight and has a hub 21 with supporting ribs 2lradiating therefrom.

The mirror housing has a side wall 3l with an opening 3| therein toaccommodate the electric motor housing 32. 'This housing is illustratedas having an annular flange Il which may be bolted or otherwise securedto the rim 34 surrounding the opening 3|, a reduced section 35 of thehousing extending into this opening. The main body structureA u of thehousing is preferably cylindrlcal and it is provided with a closed head31 at its' outward end from which extends a hollow cap Il for a purposehereinafter described.

Located inside the motor housing I form a fixed central portion Il, thishaving two disks II and -42 separated by a backing disk 43 and boltedtogether with bolts u. The general construction of each electric motoris similar and therefore only one need be described in detail. Extendingaxially from each of the disks 4I and I2 there is a xed cylindricalsection 45 and a. radial section I6. Then an outer cylindrical brushhold- I' er section 41 :is provided, this having an end The primaryelectro-,magnet 50v of each electric motor utilizes an iron cup 5|having 'an outer cylindrical wall 52, an inner cylindrical wallf, and'abase 54. A head disk 55 is illustrated as having a threaded connection56 to the outside cylindrical wall52. The head disk is secured to theange 48 by bolts 51. An air gap 56 is left at the inner portion ofthedisk 55 and between such disk and the inner wall 53. The primarycylinder is secured to a tubular stem 69 by means of a pin 10, or thlike. Secured to the cylinder 66 there are two diametrically oppositeconductor strips 1| illustrated as secured to the insulating cylinder66. An-insulating cylindrical extension 13 of the cylinder 66 carriesthe secondary or Y armature winding 14. In the reciprocation of thesecondary or armature coils as hereunder detailed the coils and theirinsulating cylindrical supports 13 move in and out of the air gaps 59and 60. Brush holders 15 are mounted in the brush holder section 41 andeach has a brush 16 threon to contact with the conductor strips 1|. Oneof these strips is connected to one end of the secondary coil14 and theopposite strip to the opposite end.

A non-magnetic cylindrical bushing 00 is lo cated within the cylindricalwalls 53 of each of the primary coil windings. This bushing also forms asuitable bearing for the hollow stems 69, each stern having a closedbase 8|. The hub 21 supporting the movable mirror is attached to theouter end of one of these stems and a counterbalancing weight 02 issecured in the other stem. Thus, the secondary or armature coils, ltheirstems and moving miror are'accurately balanced.

In order to determine the amount of reciprocation of the mirror a roda83 is attached to the counter weight 82, or if desired, tothe stem 69having the counterweight and this rod is visible through a window 94vinthe extension cover or cap 30. The rod ha: one or more indicating marks85 there n and the window 04 has one set of graduaticns 06 and anotherset 01. The set of graduations 66 is preferably graduated in thousandthsof an inch or in millimeters and where the reciprocating mirror has twodistinct movements and three positions of rest, the graduation is suchas to indicate the displacement between any two periods of rest. thatis, between the ends of the stroke and the middle position.

The graduations 61' are in units giving foreground distances, that isdistances between the camera and the foreground to be photographed.Therefore, when the mirror and the counterweight with the' rod 03lreciprocate rapidly, the marker on the rod has an elongated or spreadout appearance, and by noting the extent of this extended appearance ofthe marker line which is due to the persistence of vision, adetermination may be made of the displacement of the mirror "betweeneach period of rest and also a reading niade to determine whether such'vibration cora,1e1,1ao A vresponds to the correct displacement for theforeground distance.

In order to form a cushion for the. reciprocation of the stems carryingthe mirror and-the counterweight I provide an air cushion mechanismdesignated generally by the assembly numeral 99. (Note Fig. 1'.) Thisemploys a needle valve 9|, having a needle point 92 secured to the screwthreaded stem 93 which is threaded in a bore in an enlargement of thedisk 42, this stem passing through a perforation 94 in the wall 36 otthe electric motor housing. Th'e position of the stern is adjusted bymeans of a nut and lock nut 95, the stem having a screw driver kerf 96at the end, there being a suitable packing washer 91 under the nut. Thespace 98 defined by the cylindrical sleeve 99 located within thecylindrical portions 45 connected to the disks 4| and 42 and the ends 9|of the reciprocating stems 69 are in communication by a passage |00through the sleeve 99, a portion of the disk 42 to the needle of theneedle valve and a lateral passage |0| to the open space in the motorhousing 36 surrounding the brushes of the electric reciprocating motoroperating mirror. Hence, by adjusting the needle valve the flow of airunder compression, on

inward vmovement of the stems and under the' rarefaction during theoutward movement of these stems is controlled, thus'givingfa cushioningaction in the opposite reciprocation of the mirror audits counterweight.

The mirror and the counterweight are prevented from rotation byproviding 'the stems 69 with a keyway |05 in which a key |06 connectedwith the cylindrical bushing 80 guides the stems and hence'the mirror,and the counterweight in a. straight reciprocating motion without anyrotation, practically. Thus, the reciprocating mirror occupies asuccession of planes at right angles to the axis of the stem or at theangle to which 4the mirror is set invregard to the stem.

The mirror holder 20 for the field or'primary mirror is adjusted byproviding preferably three bosses |01 in the side I9 of the housing,threading the tubular thrust pin |06 through a boss, this being providedwith a wrench grip head |09. A retracting screw |10 extends through thetubular thrust pin and is threaded in the back of the mirror holder 20as indicated at lThis has a head ||2 with a. screw driver kerf, or thelike ||3.' A locknut ||4 is provided. By this construction, the tubularpin may be set of the cor'- rect position for the mirror and the screwH0,v

then adjusted as to the mirror holder. With three points of support forthe mirror holder lan accurate adjustment can be obtained to have thecorrect reflection of light. The path of the incidentrays-of light ofthe extreme outside of the field are indicated by lines ||5-|I6,the fulllines giving the path from the moving mirror when retracted and thedotted lines |I5'-| I6', the reflected rays when the mirror is in anadvanced or outwardly moved postion.

Thecontrol for the reciprocating electric moconsideredasnumberedLEQnEJkG, H,I, J,KandL. Theoommutatoralsocarrlesapositivelyenergized ring |24 and a negatively energized ring |25. Connecting thesegment A and the podtive ring |24 there is a leadM, and from thediametrically opposite segment G to the negative ring there is a lead N.From the segment B to the negative ring there is a lead and from thepositive ring tothe diametricallyopposite segment H there is a lead Phaving a predetermined resistance therein. From the segment C to thenegative ring there is a lead Q, and from the diametrically oppositesegment I to the-positive ring there is a lead R.. From the segment D tothe positive ring there is a lead S with a resistance, and diametrlcallyopposite the segment J, connects by'a lead T to'the negative ring. Thesegment E has a lead U to the positive ring and diametrically oppositethe lead V, connects from the segment K to the negative ring. Thesegment F has a lead W to the negative ring and the diametricallyopposite segment 'L has a lead X with a resistance to the positive ring.

The power supply lines indicated at I2C-|26' provide direct current inwhich the line |2G is indicated as positive and the lines |26 asnegative. A positive connection |21 has an adjustable rheostat |29therein and also, preferably, an ammeter |29 connecting to a positivebrush |22 bearing on the positive ring |24. The ammeter is provided witha scale which is derived empirically graduated in fore-ground feet.Therefore, the current supply may be adjustable so that the ammeterindicates the foreground distance between the camera and the fore-groundof the object or scene to be photographed. Then the proper current willbe supplied to actuate the i electric motors as hereunder indicated. Thenegto one of the secondary coils |41, and the leadsV |45-l46 to theother secondary coil |48, these connections being through-the brushholders having the brushes 16. Note Fig, 1, which bears on the conductorstrips 1| connecting to opposite ends oi' the primary coils.

The operation of the reciprocating electric motors is substantially asfollows:

The primary coils are energized with a constant current at a constantpotential and hence develop a constant magnetic flux. In the position ofthe commutator as illustrated, there is a positive connection throughthe lead M from the positive ring and a negative connection through thelead N from the negative ring to each of the Asecondary coils. 'Ihiswill cause each motor to occupy one of its extreme positions, and in thecondition illustrated, the secondary coilsrwould`berepelledandthemovingmirrorlnitsretracted position. -The commutatorrotates in the directionof the arrow |22 (note Fig. 2), and nextbringsthe commutator tsBandHinto registry withthe brushes |29 and |42.This lreversesthe'cm'nentinthelu'ush|22iue|aothenegativeleadasfromthetand positiveleadPthering|24and segmentmbutthis thethe beingtln'mhtheresistance` in the lead P. This resistance isregulated and adjusted so that in the instance given the mirror onlymoves one half of its full stroke. In the next position of thecommutator the segments C and I contact the brushes |29-I4II,respectively, the segment C being negative and the segment I beingpositive, connections being without any resistance, and the mirror ismoved to its extreme position of stroke opposite that indicated when thebrush |29 makes contact with the segment A and the brush |4 is with the-segment G. The next position reverses the polarity when the segment Dcontacts with the brush |29, the current passes through the-resistanceof the lead S, and when the segment J contacts the brush |40, such brushis negatively energized, but in this case, the current isreduced so thatthe mirror occupies its intermediate position. T'he remaining contactsand' energizing circuits may be traced out for a full rotation of thecommutator |22 and as this commutator has twelve commutator segments,the mirror has twelve periods of rest at different positions for eachrotation of the commutator, this giving six positions at the extremelimits of the stroke and six intermediate positions for the mirror.

I'he above mentioned timing of the reciprocation is on the basis thatthe moving picture camera operates at the rate of 24 panels or frames ofpictures per second, thisbeing 1440 per minute. It is usualyto thereforeoperate the shaft v| at 1440 R. P. M. and by the reduction gear thecommutator shaft |22 operates at 120 R. P. M. As it is the commonpractice to have the lens open during the rotation of the shaft through170 and closed during 190 of turn, therefore the shutter is open in thecamera a slightly greater periodthan it is closed. 'I'his gives ampletime -to shift the movable mirror during the period the lens is closedat the socal1ed closed shutter period, and therefore the moving mirrorwill be in positions of rest during the open shutter period while thephotograph is being made. lieved it will be apparent that due to themechanical construction of the opposed reciprocating electric motors andthe electrical control connections that on account of the motors beingbalanced, vibration will be eliminated and that by properlysynchronizing the reciprocation of the mirror to the timing o f the lmfeed and shutter opening that the moving mirror will occupy a diil'erentposition for photographs on each panel or frame of the moving picturelm.

In Fig. 3 I illustrate a modified type of v commutator and wiringdiagram suitable for a com dition in which it is desired simply toreciprocate the moving mirror between two extreme locations or positionsof its movement. In other words, to have the pictures on the filmalternately offset from the median line of the focal axis.

In the construction of Fig. 3 the commutator designated |55 is providedwith a commutator n'ng |56 having two segments |51|52 and a secondcommutator ring |59 having a segment |62 and a second segment IBI.Contact rings |22 and |22 are preferably mounted on the end of thecommutator assembly and these are engaged respectively by brushes|22-|22 which connect to the power supply leads |26-|26 in a mannersimilar to that illustrated in connection with1ig .2. Thelead|4oonnectsfrom thering |22 to the segment |51 and-eros lead IGI is fromsegment |21 to segment ISI, the second cross lead |42 is between segment|22 and |42. The lead |41 is from mtl tothe'ring |42. In

It is be-A this construction the brushes |39 and |40 arenot placeddiametrically opposite but are arranged to each contactvwith one of thecommutator rings.

In the operation of this commutator the brush |30 is always positive andthe brush |32 is always negative. In the position of the commutator asillustrated in Fig. 3 the brush |39 and hence the lead |4| is positiveand the brush |40 and hence the lead |42 is negative. When thecommutator rings rotate until the brush |39 contacts with the segment|58 and the brush |40 with the segment |40, the polarity of the brushes|38|40 is reversed; thus the brush |39 beconies negative and the brush|40 positive, thus reversing the polarity of the windings of thesecondary coils of the reciprocating electric motor.V In this case thecombe mounted on a shaft similar to the shaft E22,

but in this case, when'a shaft |20 rotates at 1440 R. P. M. thecommutator rings of Fig. 3 will rotate at 720 R. P. M.

Fig. 4 represents an optical' diagram to illustrate the action 'of thefixed field mirror and of the reciprocating mirror in conjunction withthe optical system of the camera. This diagram is distorted in that itillustrates the group of objects very close to the field mirror andhence to the lens in order to exaggerate the displacement with thevirtual images by the secondary moving mirror one in relation to theother, and the displacement of the images on the film, one in refer.-ence to the other. In this diagram a group of objects to be photographedis indicated by kthe numeral |10. The stationary or field mirror planeis indicated by the numeral |1|, and the various planes of the secondaryor moving mirror, by the numeral |12. In this, the intermediate positionof the mirror is designated by the letter I, the forward position of theletter F and the retracted position of the letter R.

These mirrors thus in their movement, are displaced from one position tothe other by the distance D. The lens of the camera is illustrated indiagram with the numeral |13 and the lm by the numeral |14. In thisillustration, the mean optical axis from the objects to the film may beconsidered as indicated by the optical path |15--|16-|11. In the objectsto be photographed the foreground object has in relatiorr thereto, asecond object 2 in its optical path, and 2, however being in differentplanes remote from the lens. The objects 3 and 4 are indicated in thesame plane but back of the plane of the object 2 and the object 5 isindicated displaced laterally from the mean optical axis and in a planevintermediate that of the object 2 and the objects 3 and `4. The virtualimage formed by the field mirror I1| of the above mentioned group ofobjects is designated as the primary virtual images. Therefore, fortracing the optical diagram the primary vvirtual images may beconsidered as the source of light in forming the photograph. 'Ihesecondary set of virtual images formed by the mirror in the positionl-is designated by the numeral |19. The secondary set of virtual imagesformed bythe mirror when inits forward position F by the numeral |80,and the secondary set of virtual images formed by the `mirror in itsretarded position R by the numeral Therefore, the groups of virtualimages |19, 80 and |8|, such being secondary virtual images, may beregarded as the source of light for taking three successive photographson three successive panels of the lm. For the sake of simplicity of thediagram, the path of the ray of light from the fore-ground object ofeach of these virtual images only is illustrated. Therefore, the centralray from the virtual image group |19 through the camera lens to the filmis on the line |82, and the central line from the group of virtualimages |80 is on the line |83 and from the group of virtual images |8|on the line |84.

The relative position of the images formed on the film and shownexaggerated locate the photographed images of the fore-ground objectsone from each of the secondary virtual images at the terminating pointsof the lines |82, |83 and |84 with the film |14 respectively, thesebeing indicated by the numeral The real object 2 is photographed by theray of light |82 immediately behind its foreground object but thisobject 2 of the virtual image |80 is photographed slightly to the rightof the foreground light beam 83 and slightly to the left of theforeground object light beam |84 from the secondary virtual image |8I.ment of the photographed image of the other objects of the group asdepicted by the 'secondary virtual images are indicated by the numerals3, 4 and 5 of the film plane |14. It will be seen therefore, that theobjects positioned laterally and in different planes from the foreground`actual object have different relative displacement in regard to thephotographs of the respective foreground objects photographed.

When the displacement or movement of the moving or secondary mirror isso adjusted that the relative displacement on the film of the foregroundobjects when in three different positions do not subtend an arc greaterthan seconds having reference to the camera lens and when such picturesare projected in succession, due to the resolving power of the eye, theeye cannot detect any relative movement of these objects in thesuccessive panels or frames of the picture.

Y As above described, the displacement distance on the lm of theforeground objects may be greater than 70 seconds of arc so long as itsdisplacement on the screen does not materially exceed 70 seconds of arcas viewed by the spectator.

Y Similarly, the background objects when photographed have a lateraldisplacement one relative to the other on the successive panels of thepicture but this displacement is kept so that it is within the resolvingpower of theeye to eliminate an effect of vibration of the photographedimages, but due to the function of persistence of impression in vision,-a slightly different viewpoint of the various objects in theirdifferent positions laterally from the mean optical axis and thedifferent planes longitudinally thereof,

induce the effect of bi-lateral vision. This is aided by the fact thatthe secondary virtual imagesare at different distances from the lens andhence from the film, and therefore the optical axis from the secondaryvirtual images is of a different length for each panel or frame of the,picture which causes a slight change insize of the images asphotographed on the lm. Due to these slight changes the eye is calledupon to continuously slightly change its focus as it would in naturaljvisi'on when rapidly shift ng-from observing a near to a distant objectand inter- The relative position and displacemediate objects. 'I'hisfunction of the lengthening and shortening of the common optical axis ofthe group of objects therefore calls for a corresponding change orfunction in the focusing of the eyes of the spectator when the picturesare projected on the screen and hence developes in the observer afunction'of the eyes closely similar to that in natural bl-lateralvision in viewing objects at different distances from the spectatorandhence aids in producing .the illusion of normal bi-lateral vision ofprojected moving pic- -numeral 200 has a forward table section 20| witha tongue 202, this being dove-tailed and forming a guide for thereciprocating motor .assembly. The rear section 203 of the supportingtable is lower than the forward .section 20| and is adapted for mountinga camera having suitable guides on which the camera designated by thenumeral 204 may be mounted. The particular type of table support for.the camera is designed in accordance with the particular `camera to beused with the rest ofthe. equipment. Extending laterally from the camerasupporting table 203 there is a commutator table supporting section 205.Thus the various table sections 20|, 203 and 205 are formed integral andhave a tripod mounting 206 for attaching the'supporting table to atripod. The camera isvclamped by a clamping. nut 201 as is the usualpractice. Slidably mounted on the forward section 20|V of the supportingtable I employ'a base' plate 208 .which forms a mountingfor the mirrorhousing 209, which housing is substantially the same as shown anddescribed in connection with Fig. 1 and employs a fixed mirror 2|0mounted substantially in the same way as above described. This mirrorhas an opening 2|| (note Fig. 6) to which is connected the electricmotorhousing 2|2. This housing has an end wall 2`|3. Confined within thishousing are the two primary electro-magnets 2|4, eachl of which has aniron cup 2|5 and each is provided with a screw threaded headdisk 2|6.Within each cup there is the primary winding 2|1. cage 2|0 isillustrated as having end flanges 2|9 secured to the head disk 2|6 andconnecting webs 220. Bushings22| are provided inside the cups of theprimary magnets and slidably mounted in these bushings there is thehollow `stern 222 which supports the mirror holder 223 at its outer end.The mirror holder has a guide lug 224 with a guide socket 225 whichslides over the xed guide pin 226 secured to the outer cup 2|5, 'andthus prevents rotation of the mirror in its reciprocation. Attached tothe stem 222 I employ an insulating spool 221. This has enlarged drumsections 228 at each end on which is wound themoving armature windings229. These windings lead to terminals 230 from which flexible wires 23|form the lead-outs. There are two compression springs 232 each housed in.the drum portions of the spool and bearing against the central porofreciprocation o f the stem 222.

A spacing tion and against the ends of the bushing 22| and the innerwall of each ir'on cup 2|5. These springs are alternately compressed andexpanded during the reciprocation of the spool, the moving coils, andhence the mirror. An annular space 233 is left inside of the head disks2|6 and the inner end` portion of the windings 2H to accommodate thereciprocation of the drum section 220 of the spool and hence of themoving armature coils.

The path of light in the direction of Fig. 6 is similar to that of Fig.l, the mirror being indicated on the diagram and hence need not be morefully described.

A stroboscope arrangement designated by the assembly numeral 240 isutilized to visibly show the extent of reciprocation of the mirror, thatis, the mirror displacement, and also, thus to indicate when the deviceis operative and the mirror is properly reciprocated. This employs ancon tube 24| (note Fig. 6), which tube is l housed within a hollowextension 242 of the motor housing 2|2. This extension is connected tothe end wall 2|3, and the neon or a similar tube is attached to the endcover 243 (note Fig. 5). The tube extends within the tubular stem 222lwhich carries the mirror, which stem has Aa transverse slit 244 whichslit is visible throughare two spaced lines indicatedthrough the windowand on the scale which shows the distance This distance may be varied ina manner hereinunder detailed:

The outer end 250 of themotor casing 2|2 forms a housing for thetransformer 25| which energizes the stroboscope, the wiring for suchbeing illustrated in Fig. l2.

The motor housing 2|2 has a'lateral extension 252 (note Figs. 6 and 8)which houses the rheostat' 253.

the. lower portion of the housing 252 and on the cover plate 251 islocated a control knob 256. (Note Figs. 'l and 8.) This control knob hasa pointer 259 operating over a sca1e260. A partial partition 26| (noteFig. 8) separates the lateral extension 252v into a lower and an upperpart. and in the upper part there is an ammeter 262. Such ammeter has 'apointer 263 operating over a scale 264, which scale can be graduatedboth in an ammeter reading and also in lineal distance, such being aso-called foreground distance measurement, sothat when the rheostat isadjusted, the ammeter indicates on the scale the photographic distanceby-which the stroke or throw Ao1' the mirror is adjusted. Connectingelectric leads between the rheostat and ammeter are indicated at 265. 4

The commutator assembly designated generally by the numeral 210 isillustrated particularly in Figs. 5, 9, 10 and 11. Such assembly has ,abase of the main supporting table 200. A pedestai 212 extends upwardlyfrom the base and has the commutator housing 213 mounted thereon. This`housing is preferably cylindrical on the inside and has a closure head214 facing towards vthe camera and a cover plate 215 on the oppositeside. The commutator shaft 216 has bearings in the head 214 and in thecover plate 215. Such shaft also has a bearing 211 in a gear casing 218attached vto the closure head 214. This gear cas-Y ing forms a bearingfor the drive shaft 219 which has a large gear 280 meshing with a pinion28| on the commutator shaft 216. I'he shaft 219 has a telescopicextension 282 connected by a key-way and key 283, such tubular extension282 forming part of the crank shaft of the camera 204. (Note Fig. 5.)This telescopic extension accommodates the transverse slide movement ofthe camera on its support without disconnecting the shaft of the camerafrom the commutator drive The commutator designated by the assemblynumeral 285 has an insulating disk 286 (note Fig. 9) attached to theshaft 216, and on this disk is mounted the commutator segments 281 andthev two commutator rings 288 and 289. The brush supporting disk 290 isrotatably mounted/in the cylindrical part of the commutator housing 213and has a pair of brushholders 29|, each havingI a brush 292 slidablymounted therein, each brush being pressed outwardly 4by `a spring 293.in order to make a good electrical contact a slack wire 294 is attachedto the base of the brush holder and also to each brush, the brushesbearing on the two commutator rings 288 and 289.

The commutator segments, of which there are two, have their ends spacedapart and insulated from a dead or non-connected metal contact 49 piece295 (note Figs. 11 and 12). These are of such shapeand the same size asthe commutator apparatus of Fig. 6 and its assorgated gures employs asupply line 305 from which there are supbrushes 296 which bear-on thecommutator segments 281. These brushes are pressed in contact with thesegments by pressure springs 291 (note Fig. In order to provide foradvancing andretarding the commutator brushes to regulate the time ofthe movement of the mirror in relation to the shutter of the camera, the

vcylindrical part of the commutator housing is provided with a slot 298(note Fig. 10), through which extends a handle 299 which is secured tothe brush supporting insulating disk 290, this handle being movable fromone end to the other of the slot. An electric cable 300 carries theelectric leads from the commutator housing, such takingoi from thecovaer cap 215 to a plug 30| which may be plugged in the extension 252housing the rheostat 'and thus form an electric connection t0therhostat. f

The wiring diagram, Fig. 12,'.ior vthe simplified ply leads 306 to eachof the primary coils 2I1.

The supply line also leads to therv brushes 292.

which contact with the commutator rings 288 and 289. vBetween theserings are connections 301 and 308 with the two commutator segments 281.

From the commutatolbbrushes there are leads 309 one of which has therheostat 253 and the ammet'er 262 in circuit. These leads supply thear-` mature coils 229 Arwhich are arranged in series.

Thus, on each halt. rotation of the commutator, the polarity of thearmature coils 229 is reversed..A This gives a push and pull effectbetween the. primary coils or magnets and the armature coils.

leads 309, this circuit having a transformer 25| therein, the secondaryof which is connected to the neon tube 24|, there being a condenser 3|in the primary circuit controlling the stroboscope.

The action of the stroboscope is to become energized and thus the tubebecomes illuminated at the end of the mirror strokes and hence the twoend lines formed by the light passing through the slit 244 in the.mirror supporting stem are quite well defined and indicate the ends ofthe stroke.v Thus, the length of the mirror stroke may be read on thevisible scale through the window 245. The stroke may be varied byregulating the rheostat which controls the supply carriage to thearmature coils and as above mentioned, the current supply may be read onthe ammeter 262 which is graduated to show the distance at which thephotograph' is being made, and therefore the operator, by knowing .thecorrect distance, may correctly set or regulate the stroke of themirrors and this may be checked by a readl ing Ldetermined by thestroboscope. 1

It is essential to obtain a correct timing of the reciprocating mirrorand the shutter and nlm of the camera so that when the shutter is in theopen position and the film stationary, the secondary moving mirror willbe at a position of rest. w 4 1h'e interior mechanism of the cameraconnects the nlm feed and the shutter and also the shaft of Fig. 2 and282 of Fig. 5 in synchronized operation. A simple way of determining ifthe shutter -is open when the moving l mirror is at rest is by employinga second stroboscope. This is designated by the assembly numeral 320.(Note Figs. 5, 12 and 13.) One way of connecting this second stroboscopeis to provide a silver conducting band 32| on .the outside of thereciprocating tube 222. This may be located close to the slot 244through, which the light of the iirst stroboscope lamp 24| is visible,this being observable through theV window 245 as above mentioned. Theouter end 250 of the motor casing 2|2 is provided with a slot 322 andoperating on the outside of the casing in suitable guides there is amovable Vernier block 323 which is actuated by a screw 324 operatingthrough the fixed threaded block 325. Secured to the Vernier block thereare two brush arms 326 having contact points 321. (Note Figs. 12 and13.) These `are connected to leads 328 from the n- 06 in a suitablecurrent source. These `nect to a second ,stroboscope transformer 329from a secondary of which there are exible leads 330 which connect V tothe second stroboscope lamp 33|. Forftlrreisake of conven- `ience anoutlet plug 3 32 is gio'nnected into the housing 250 and theilexible'leads may be led.

lens, the shutter and the lm gate so as to'be visi' The stroboscope lampwhichis preferably a neon lamp is placed in the opticalv path of the iible tnreuzh the entire apparatus .when the shut* the mirror mechanismwith the camera shutter.

A change of the brush holder position on the commutator obtains therelative adjustment of the reciprocating mirror to obtain a propertiming.

The manner of operation is as follows: When the camera and thereciprocating mirror is operated at photographingspeed, in the set-upillustrated, a bridging contact is lmade between the contacts 321 andthe silver conducting band on the reciprocating tube 222 at the extremeend of a stroke which causes the energizing of thetransformer 329.Therefore, there is a flash of light in the second stroboscope lamp 33|located in the camera when the mirror is at one extreme end of itsstroke and stationary. The cameraman therefore may look through thelarge win? dow of the camera box shown in section in Figs. 1 and 6, andif he observes the flash of the light he will know that the shutter isin its open position.

' Should there be no light visible from this second stroboscope lamp hewill know that the shutter is either ahead of or behind the mirror inits action.. The brush holder may then be moved by the-handle 299 (Figs.5 and 1o), and by the adjustmentof the brushes in the commutator ofFigs. 2 and 3 to secure the correct timing of the shutter and movingmirror. The commutator for energizing the electric reciprocating motoris then Aso adjusted that the cameraman observes a light of the greatestintensity which in` dicates rthe correct synchronizing of thev mirror,such being in -a stationary position while the -shutter is open andhence the film is in its stationary position.` 'Ihe movement of thevemier block 323 also indicates the length of the total stroke of themovable mirror.

For convenience of set-up a single neon tube energizing transformer maybe utilized and a removable connection may be m'ade for energizing thissingle transformer either through the commutator or suitable, powersource, for when making a test to secure the correct timing of themoving mirror and the-shutter it is not necessary to use the iirst stroboscope which indicates the length of the reciprocating stroke of themirror, and afterv the .correct timing is secured, the secondstroboscope may be disconnected from the stroboscope-circuits. Thecontact points 321 should be carefully adjusted so that they form thebridging contact with the silver band 32| at thesame position at the endof the stroke lno matter whether the rheostat 253 is adjusted to give along or a short stroke to the lmoving mirror. The construction of thecontact pointsis illustrated in detail in Fig. 14 in which the bent overside edges 333 hold a carbon block 333, such blocks forming the contactfor the silver band 32|.

It is obvious'that the first and second stroboscope lamps may beutilized .in connection with the arrangement of Fig. 1 in which thereciprocating mirror mayA occupy three distinct stationary positions ortwo positions in accordance with whether the commutator set up of Figs.2 or 3 is utilized.

In order to complete the optical diagrams I show in a diagrammaticmanner the camera shutter-designated bythe numeral 340 in Figs. 1,

6 and 4, but as above mentioned, I make no change in the interiorconstruction of the camera or the manner of operating the shutter, theinterl arcaico 'rms in mateur feed for the nlm, or in the focusing ofthe camera lens. 'Ihe actuation of the camera.V either by an electricmotor, which is the common practice, or by a hand crank developes theco1'- rect synchronized operation of the shutter, the nlm feed, and alsothe drive to the commutator which controls the reciprocating electricmotor.

It is generally considered that two eyes separated by what is termed thepupillary distance are necessary to obtain the perception of depth orperspective, but this is not always the case. A very` minutedisplacement of the optical axis of one eye gives a similar result, asit is well known that people with only one eye, for instance, some notedaviators, are able to detect depthand distance-due to motionalperspective. With my apparatus and manner of procedure I mechanicallyobtain this motional perspective, and the resulting picture on thescreen exercises all the.

'the invention as dened by the appended claims.

I claim: y A 1. In a device as described, the combination of asupporting table having a iirst set of guide ways, -a motion picturecamera laterally movable thereon., a second set of guide ways, a mirrormounting adjustably mounted on the second set of guide ways, such'mirror mounting having a xed and reciprocating mirror, an electric motorattached to the mirror mounting and operative to reciprocate thereciprocating mirror, the said mirror mounting `having an openingalignable with the lens of the camera, the camera having a shaft, thesupporting table having a housing with a commutator therein, a drivefrom the camera shaft to the commutatox' and an electric circuit ,forthe electric motor including a field coil and a moving secondary coil,the secondary coil having in its circuit a commutator, a rheostat, andan ammeter.

2. In a device as described, a motion picture camera having a lens and amovable shutter combined with a changeable optical reflector operativelyassociated with the camera lensvand the shutter, a stroboscope having alight observable through the camera lens when the shutter is in an openposition, means to operate the camera and optical reflector at normalphotographing speed, means operatively connected with the opticalreflector to energize the stroboscope whereby observation of the lightthrough the lens may de-. termine the correct synchronism of the shutterand optical reflector, and means to relatively vary the timing oi' theshutter and the optical reflector to secure correct'synchronism.

3. In a device as claimed in claim ll, a stroboscope operativelyconnected to the reciprocating mirror and including an electric circuitenergized through the make and break of the circuit connected to thecommutator.

4. In a device as described in which a motion picture camerahas itsoptical system, an intermittently acting iilm moving mechanism and ashutter combined with. a reciprocating mirror podtioned to reflect lightdirectly to the opticalA system of the camera, said mirror having amirror holder with an elongated central shaft, the4 mirror beingsymmetrical as to the shaft, the axis of the shaft'being in the opticalcenter of the mirror, a Support for the shaft having elongated bearings,means to'reciprocate the shaftand to bring the shaft and mirror to restin synchronism with the operation of the camera whereby the positions ofrest of the mirror during the periods of photog raphy are always exactlyparallel and the mirror is prevented from warping or flexing fromvibration the axis of the optical system of the camera and the axis ofthe reciprocating mirror being at an angle one to the other.

5. In a device as described and claimed in claim fi, a iixed structureas regards the bearings of the shaft having a window, a reciprocatingsecond shaft like element operatively connected to the shaft of themirror mounting to reciprocate simultaneously therewith and to bebrought to rest during the periods of rest of the mirror, scalesassociated with the window structure and the second shaft to measure thetravel of the second shaft and hence of the mirror and a stroboscopetype of lamp positioned to illuminate the scales with means to energizesaid lamp only when the mirror is at rest and thereby enable determiningthe stroke of the mirror.

6. In a device as described and claimed in claim 4, a second shaft likeelement having means to actuate the same in synchronism with thereciprocation of the mirror and to bring said shaft to rest duringstationary periods of the mirror, an adjustable electric contactconnection including a conductor on the second shaft, a stroboscope typeof lamp with an electrical connection whereby the lamp may be positionedthe camera back of the shutter and means toenergize the said stroboscopelamp to secure a flash of the lamp during periods of rest of the mirrorwhereby on observation of the iiash of the lamp in the i mirror adetermination may be made of the correct synchronism of the mirror andthe shutter and film feed of the camera.

7. In a device as described in which a motion picture camera has itsoptical'system, an intermittently operative nlm moving mechanism and ashutter combined with a reciprocating mirror for reciprocation in aiixed structure, the mirror being positioned to reflect light to theoptical system of the camera, means to synchronize the reciprocatingmovement of the mirror and the operation of the camera whereby themirror has periods of rest during the photographing period of thecamera, a reciprocating element operative in synchronism with thereciprocation of -the mirror, a scale associated with said element toindicate the length of Ithe stroke of; the mirror, a stroboscope typeVof lamp positioned to illuminate said scale and means. to energize saidlamp only at the periods of 'rest of the mirror and means to l vary thelength of .the stroke of the mirror the axis of the optical systemu ofthecamera and the axis of the reciprocating mirror being at an angle oneto the other. 'V

8. In adevice as'described in which a motion picture vcamera has itsoptical system, an intermittently operative film moving mechanism and ashutter combined with. a reciprocating mirror for reciprocation in afixed structure, the-mirror being positioned to reflect lightI to theoptical system of the camera, means to synchronize the reciprocatingmovement of the mirror and the operation of the camera whereby themirror lhas periods of rest during the photographingperiod of thecamera, a reciprocating element operative in synchronism with thereciprocation of the mirror, an electrical connection including amovable brush and a conductor onthe said reciprocatingv element, astroboscope type of lamp having a.

connection whereby such lamp may be placed in the camera back of theshutter and means to energize said lamp with current through the saidelectrical connection whereby the lamp is periodically energized andmeans to `relatively vary the timing of the camera action and of thereciprocating mirror to secure correct synchronism `for photography, theflash of the lamp being observable by the reilection from the mirror theaxis of the optical system of the camera and the axis of thereciprocating mirror being at an angle one to the other.

9. A motion picture apparatus comprising in mirror are directed to acamera and means to reciprocate the second mirror and to bring saidmirror to rest'to produce in the camera a sequence of laterally offsetimages on successive panels of a film the axis of reciprocation of thesecondary mirror being positioned at an angle to the axis' of theoptical system of the camera.

10. A motionpicture apparatus comprising in combination a supportingstructure with a first guideway adapted for the mounting and lateralmovement of a camera, a second guideway having a dust-proof housingadjustably mounted thereon, said housing having a first plane glasswindow for incident light and a second plane glass window for reflectedlight, adapted for alignment with the optical system of the camera, aiirst mirror fixed as to the housing and camera to receive the incidentlight, a secondary relatively small reciprocating mirror positioned toreflect light from the fixed mirror through the second window to Y thecamera, means to reciprocate the second mirror and to bring such mirrorto rest to cause a sequence of lateral displacements in the camera of aray of light from an object to be photographed the axis of reciprocationof the secondary mirror y being positioned at an angle to the axisl o`fthe optical system of the camera.

11. In a device as described in which Va motionl picture camera. has itsoptical system, an intermittently acting film moving mechanism and ashutter combined with a reciprocating mirror poi sitioned to reflectlight directly to the optical .system of the camera, said mirror havinga mirror holder with an elongated central shaft, the mir-y ror beingsymmetrical to the shaft, the axis of the shaft being in the opticalcenter of thelmirror. a complementary similar shaft, a support for bothshafts having elongated bearings whereby the shafts are in axialalignment, means to simultaneously reciprocate both shafts inl oppositedirection and to bring both shafts to rest in synchronism with theoperation of the camera whereby thel positions of restvof the mirrorduring the periods of photography: are always Jexactly parallel and themirrors prevented .from warping or flexing from vibration, the said twoshafts compensating as 'to vibration, the axis of the optical 'system ofthe camera and the axis of re- `an angle one to another.

l WIILIAM"F. ALDER.

